TROUBLESHOOTING: How to cool a warm cryo

It's a Mohs Gnome morning.

You forgot to plug in your cryo before you went to bed, or the staff forgot to turn on the in-office cryo.  Maybe there was a power outage in the middle of the night.  For whatever reason, it's morning, your cryo is warm, and you don't have the luxury of waiting 3hrs for it to get cold.

Take a deep breath.  Here's what you need to do.

[optional] The Ice-Bag Method - MN

If your job is ≥30min away, you may want to consider using the Ice-Bag Method to start cooling your cryo while you drive.

Place bag directly on microtome.

STEP 1: Break the block of dry ice into smaller chunks. 

STEP 2: Dump everything into a plastic bag and double-knot the handles.

STEP 3: Place the bag directly on the microtome.

STEP 4: Close the lid, cover the cryo, strap it in, and get to that office!  (drive safely, of course)

30min of driving will give you a -13°C headstart on cooling, and the plastic bag will have prevented most of the frost from building up on your microtome.

The Standard In-Office Method: Dry Ice and LN₂

Most of the time, you’ll live close enough to your job that it’s best to just take your dry ice directly to the office and plug in your cryo ASAP. 

STEP 1: Get your knife into the machine so it can start cooling right away.

STEP 2: Balance the chunks of dry ice on the microtome.  Some well-placed damp paper towels will prevent the chunks from shifting and will act as ice cubes once they freeze up.  –EM, TR, CD

Caution: Make sure the dry ice doesn’t rest against the walls of the cryo or

else the Freon in the tubes will freeze solid and ruin your machine.  –BP

STEP 3: Slowly pour LN₂ over the microtome and knife.  Close the lid.  You will have to repeat this step several times before the machine is cold enough. 

The chunks are usually bigger. These have been sitting in a bag for a few hours.

Pro Tips:

Fill the "bowl" and ball joint socket with LN2.

-Use a damp paper towel to form a cup next to the knife and fill it with LN_2.  Also, keep pouring LN₂ into the socket for the ball joint. –GS

-Place the knife on the cold bar while the machine cools.  If you have a small knife, you can dunk it into the cry-ac to rapidly cool it.  You can cut with a warm machine as long as your knife is cold, but you have to be fast and use freeze spray between each cut. –GG

-Use the Quick Freeze by turning the dial clockwise from 0, where it’s usually at,
to 3. –BP, EM

-Cover up the thermostat as much as possible with paper towels/gauze so that when you pour in the LN_2, the thermostat doesn’t read the temp and shut off the machine. Not all machines have working thermostats though! –KM

-Use magic. –CS (Don’t bother asking her for the spell.  I’ve already tried.)

-Test for warm spots with dabs of OCT. (should freeze in less than 5 sec) –GG

-You can double stack two Styrofoam cups in the cryo under the blade or near the machine.  The double layer reduces the rate of evaporation of the LN₂  and allows for a cooler in-machine ambient temp. –GG

[experimental] The LN₂ Geyser Cup - GG

When you cut in a warm machine, the air makes the block sticky.  Get a urine cup, fill it with LN_2, and poke a hole in the lid.  The LN₂ will rise from the hole in a slow geyser.  Place the cup under the blade and direct the geyser towards the block.  This keeps you from needing to spray between cuts.